css.css - add mobile styling

added a basic media query that gives mobile styling for devices
under 500px X or Y

-- lynn
css.css - change #main width to a percent

Change the width of #main to a percent so it scales better on
various resolutions. The exact value of the percent is probably
off by quite a bit, though.

-- lynn
css.css - indent lists

added 20px of padding left and right of <ul> tags